This project involves comparative morphologic studies in normal dogs and a family of dogs with spontaneous hereditary patent ductus arteriosus developed at the institution. Embryologic and microscopic studies will be carried out to characterize the embryogenesis of the disorder which preliminary studies have shown to be due to a structural defect in the wall of the ductus in dogs. Pulmonary vascular disease and plexiform lesions secondary to PDA leading to pulmonary hypertension will be studied as an animal model to help determine the pathogenesis of similar changes occurring in some humans with hyperkinetic congenital heart defects. Particular emphasis will be placed upon the morphogenesis of the plexiform lesions since the pathogenesis of these structures is unknown and they are commonly seen in various forms of severe pulmonary hypertension in man. The sequence of development and reversibility of pulmonary vascular lesions will be studied by periodic lung biopsies before and after unilateral pulmonary artery banding in neonatal dogs with PDA and later closure of the ductus.